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BOSSED SILICON CAPACITIVE ABSOLUTE PRESSURE SENSOR

Publishing Venue

Motorola

Related People

Steven Chen: AUTHOR

Abstract

A bossed silicon capacitive absolute pressure sen- sor can be fabricated to provide the following perform- ance and cost advantages: (1) Increase pressure sensitivity For the prior art shown in Figure la, the pressure sensitivity is proportional to LYh: where L is the linear dimension of the diaphragm and h is its thickness. How- ever, there is a limit of improving the sensitivity by SC& ing due to diaphragm buckling caused by internal stress. Both larger L and smaller h increases the likelihood of buckling. The proposed improved design uses smaller thin areas by etching the diaphragm peripherally (Fig- ure lb and 2). Diaphragm bending will be primarily con- centrated on the small thin area, thereby extending the sensitivity limit without causing buckling.

Copyright

Motorola Inc. March 1993

Country

United States

Language

English (United States)

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MOTOROLA INC. Technical Developments ydume 18 March 1993

BOSSED SILICON CAPACITIVE ABSOLUTE PRESSURE SENSOR

by Steven Chen

A bossed silicon capacitive absolute pressure sen- sor can be fabricated to provide the following perform- ance and cost advantages:

(1) Increase pressure sensitivity

For the prior art shown in Figure la, the pressure sensitivity is proportional to LYh: where L is the linear dimension of the diaphragm and h is its thickness. How- ever, there is a limit of improving the sensitivity by SC& ing due to diaphragm buckling caused by internal stress. Both larger L and smaller h increases the likelihood of buckling. The proposed improved design uses smaller thin areas by etching the diaphragm peripherally (Fig- ure lb and 2). Diaphragm bending will be primarily con- centrated on the small thin area, thereby extending the sensitivity limit without causing buckling.

Non-linearity is inherent in the prior art (Figure la) because two electrodes are not in parallel during opera- tion. To achieve the best possible linearity, a capacitive sensor is usually designed by limiting its operation pres- sure range so that two elecrodes are nearly parallel dur- ing operation. The proposed boss design allow the mov- able silicon electrode ret&ins nearly parallel without much bending, while the edge of the diaphragm bends to a larger extent (Figure lb) to provide diaphragm movement.